Is it normal for these CRD's to have a hiss upon acceleration? I had a low boost code and cleared it, then I replaced the boost hoses with the fancy silicone ones

I drove it around sounds exactly the same. It did not generate a code at all now. And still makes the same sound. I'm unsure the correlation here.

I also held brake and applied throttle to make boost while sitting still and did not hear any hiss, strange. I did it fairly aggressively but don't wanna stress torque converter too much.

I heard this same hiss from a TDI I have and there was a loose boost hose. Thoughts?

I dont think a hiss is normal. It would be relevant for the people here that can help you to know if the egr system is installed and functional on your jeep.
Also, not entirely sure, but with a stock tune the system may not allow boost with the brake applied...

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2005 KJ CRD SOLD in 2021
V6 Airbox, Samco Hoses, Provent
Weeks 1&2, Thrush Glasspack
Facet Fuel Pump, Secondary Fuel Filter
ARPs, 188 Degree Thermostat
GDE Eco Tune Full Torque
OME 1.5", JBA A-Arms and Top Plates
245/75/16s, Spidertrax

2005 crd 72k miles. Egr exists but GDE tuned so it’s turned off.

That’s interesting about brake thing never heard of that.

I also did a boost leak test with compressed air and was only able to get about 10psi because wrong size fittings. Anyways there was no noticeable leak or hiss at 10 psi. Since hoses are new they are only thing that would expand and fail. The intercooler is rigid I’d think it would show the leak under any pressure. I didn’t hear any leak!

I do plan to remove egr system at some point and see if it helps. I wouldn’t think you could hear it leaking past egr valve if it was.

The hiss is kind of subtle not super loud. But no codes so far?

On your Jeep is there any noticeable hissing type sound?

The only engine sound I hear with acceleration is a slight turbo whine. The EGR can still leak boost with the electrical turn off with a tune but I don't think it would make much of a hissing sound without a code and doubt it would even with a code.

Since it isn't showing a code now I would take a close look at the turbo to air hose which could suck air in and make a hissing sound and wouldn't hurt to check it anyway. See this topic that covers that hose etc and at end there is a silicone hose available now from Sasquatch. This hose of course does not carry boost pressure.
viewtopic.php?f=5&t=60636

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05 Blu LIM, OME GDE Tbo, wk II 245/75/17, KC Lights, bull bar, 195K H TC
05 Blu Lim, Dayton, GDE HT, 255/75/18 , 210K , H TC
06 Bla Lim, GDE Eco, Destination AT 245/75/17, 151K, H TC
06 D Khaki Lim 126K wkII Eur TC
05 D khaki Lim 145k refurbishing
All CRDS: Fumoto, Lift , Fan Shroud mod, fuel head Gen II, SAMCOS,self TB, 2 Mic filt, Hayden

Hmm, as far as I can see it looks pretty good, some seeping and it's pretty nasty would be hard to see much of a tear or hole.

I'm not sure it would hiss like that either, the vacuum isn't very high like -1psi or whatever?

I don't think its real likely but the vacuum is higher than you would think try undoing the hose from air filter top and put your hand over it. Of course if you do and can feel the vacuum and its doubtful it has a significant leak.

I can't think of too many there sources though . Maybe a leak in vacuum system somewhere and that would likely also affect boost.

Remember a relatively small leak makes more noise than a large leak. Just like barely opening a faucet versus opening it wide open.

Another thought would be an exhaust leak but I would think that would also cause an odor or smoke etc.

_________________
05 Blu LIM, OME GDE Tbo, wk II 245/75/17, KC Lights, bull bar, 195K H TC
05 Blu Lim, Dayton, GDE HT, 255/75/18 , 210K , H TC
06 Bla Lim, GDE Eco, Destination AT 245/75/17, 151K, H TC
06 D Khaki Lim 126K wkII Eur TC
05 D khaki Lim 145k refurbishing
All CRDS: Fumoto, Lift , Fan Shroud mod, fuel head Gen II, SAMCOS,self TB, 2 Mic filt, Hayden

GDE mentioned exhaust leak also. Seems it would make a lot of noise though not just a hiss. Weird

Yea I can try the air box hand thing it should kill the engine if it’s sealed up

Same a TKB4, just some turbo whine. Wouldn't describe the sound as a hiss.
It likes to whistle when the throttle comes off....

_________________
2005 KJ CRD SOLD in 2021
V6 Airbox, Samco Hoses, Provent
Weeks 1&2, Thrush Glasspack
Facet Fuel Pump, Secondary Fuel Filter
ARPs, 188 Degree Thermostat
GDE Eco Tune Full Torque
OME 1.5", JBA A-Arms and Top Plates
245/75/16s, Spidertrax

I don’t hear any whistle surprisingly. Maybe the turbo isn’t acting right but it seems to run good with good torque and so far no codes after hose replacement. Old hose for turbo outlet had some suspicious tape on it lol. Who knows.

other than rechecking boost hose connections especially if you have the two piece intake elbow, short of putting it on a DYNO and listening with load while it is still and you could stand beside it with mechanics stethoscope which isn't safe I don't know anything else to suggest. If it runs good I don't think I would worry about it unless it starts running bad or throws other codes

Make sure and tell us what it was if u find cause.

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05 Blu LIM, OME GDE Tbo, wk II 245/75/17, KC Lights, bull bar, 195K H TC
05 Blu Lim, Dayton, GDE HT, 255/75/18 , 210K , H TC
06 Bla Lim, GDE Eco, Destination AT 245/75/17, 151K, H TC
06 D Khaki Lim 126K wkII Eur TC
05 D khaki Lim 145k refurbishing
All CRDS: Fumoto, Lift , Fan Shroud mod, fuel head Gen II, SAMCOS,self TB, 2 Mic filt, Hayden

It does run good and I think I'm not going to worry about it, lol. It has not thrown a code and drove it around all day. Runs great, AC ice cold, I'm happy.

I think the hissing could have been separate problem from the previous underboost code, now it's gone after replaced boost hoses with the silicone ones.

I will definitely post an update if I find something in the future, thanks!

Maybe a long shot but this did happen to on of my CRD's. I chased a suspected boost leak for a long time. Sounded like a hiss coming from the upper passenger side of the engine. Mine never through a code though, nor displayed performance issues, just the hiss. New hoses, etc. rechecked all connections, pressure checked the inter-cooler all with no success. Very annoying. Then one day got a wiff of burning metal and the hiss was louder. The viscous heater bearing had failed and was dying a slow death for quite awhile making the hissing sound I mistook for an intake leak. The viscous heater had been unplugged for years but the pulley still spins basically as an idler. The whole heater assembly is now bypassed and removed, replaced by my design idler pulley assembly so the same size belt remains.

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2006 KJ Sport CRD, 2006 KJ LTD CRD, 2013 Subaru BRZ 6spd., 1994 Ford F150 XLT, 1969 Dodge Charger R/T 4spd. (Yes it's a Hemi).

Got any pictures?

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Supporting Vendor and Moderator of LOST
05 Jeep Liberty CRD Limited
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount
98 Dodge Cummins 24 Valve

But mine only hisses upon throttle application mostly above 2k. Not just cruising 2k. Definitely boost related or maybe exhaust. Related to throttle and turbo spool.

I’m unsure how this viscous heater works I did notice a pulley not spinning upper left of engine is that what that was? It works by friction heating? Weird

Because its speed varies with engine rpm, it can seem it is throttle related. Not saying that is your issue, especially if yours threw a code, but something to keep in mind.

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2006 KJ Sport CRD, 2006 KJ LTD CRD, 2013 Subaru BRZ 6spd., 1994 Ford F150 XLT, 1969 Dodge Charger R/T 4spd. (Yes it's a Hemi).

I do. I will try to get them posted later tonight, with a small write up.

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2006 KJ Sport CRD, 2006 KJ LTD CRD, 2013 Subaru BRZ 6spd., 1994 Ford F150 XLT, 1969 Dodge Charger R/T 4spd. (Yes it's a Hemi).